The present invention relates to a surge absorber installed in an electronic device or other electrical apparatus that a voltage surge can damage. The surge absorber comprises a semiconductor surge-absorbing element that can prevent a malfunction of the electronic device caused by a voltage surge. More particularly, the present invention relates to a chip-type surge absorber adapted to be mounted directly on the surface of a printed circuit board.
A surge absorber is usually connected to a pair of input lines of an electronic component of a communication or electronic device. The surge absorber operates at a voltage higher than the service voltage of the electronic component. More specifically, the surge absorber is a resistor that in normal operation has a high resistance at any voltage lower than its service voltage. When an impressed voltage becomes higher than the service voltage, the resistance of the surge absorber drops to no more than several tens of ohms. Thus, when a voltage surge, as from a nearby lightning bolt, is applied to a surge absorber protecting an electronic component, the surge absorber is instantaneously actuated to absorb the voltage surge. This actuation prevents the voltage surge from traveling through the electronic component, thereby preventing the voltage surge from causing damage to the electronic component.
A surface-mounted chip-type surge absorber is known that employs a semiconductor surge-absorbing element, generally a thyristor. This surge absorber comprises, in addition to the semiconductor surge-absorbing element, a pair of electrode plates and a resin body. The resin body covers the surge-absorbing element and leaves exposed each of the terminals of the electrode plates. One end of each electrode plate is connected to each of upper and lower electrode surfaces of the surge-absorbing element. Since the other ends of the electrode plates are located on a plane, this surge absorber can be mounted directly on the surface of a substrate.
In the surge-absorbing circuit of a communication line such as a telephone circuit, a surge absorber is connected between the input lines, and a plurality of surge absorbers dissipate any voltage surge impressed on either one of the input lines.
For example, a chip-type surge absorber is generally connected to a pair of input lines that are in turn connected to an electronic component. When a surge-absorbing circuit uses a surge absorber that incorporates a conventional single-semiconductor surge-absorbing element, two or three surge absorbers must be mounted on the substrate. Mounting a plurality of surge absorbers rather than one requires both a larger area for mounting and more installation labor.